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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 25  |  Issue : 3  |  Page : 121-126

To study the effect of site and size of tympanic membrane perforation on graft uptake rates and hearing improvement in type I tympanoplasty using sliced conchal cartilage reinforced with temporalis muscle fascia and temporalis muscle fascia alone


Department of ENT and Head Neck Surgery, GMC, Amritsar, Punjab, India

Date of Submission14-Oct-2018
Date of Decision06-Feb-2019
Date of Acceptance26-Mar-2019
Date of Web Publication18-Oct-2019

Correspondence Address:
Ravinder Singh Nagi
E-130, Ranjit Avenue, Amritsar, Punjab
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/indianjotol.INDIANJOTOL_94_18

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  Abstract 


Aim: To study the effect of site and size of tympanic membrane perforation on graft uptake rates and hearing improvement in Type I tympanoplasty using sliced conchal cartilage reinforced with temporalis muscle fascia and temporalis muscle fascia alone. Materials and Methods: In this retrospective study, a total of forty patients presenting with dry central perforation with intact and mobile ossicular chain and conductive type of hearing loss, visiting the ENT outpatient department of Government Medical College, Amritsar, were included. They were randomly divided into two groups of twenty patients each, with Group I patients undergoing Type I tympanoplasty with temporalis muscle fascia and Group II patients with sliced conchal cartilage as graft reinforced with temporalis fascia. A pure-tone audiometry (PTA) was done within 1 week prior to the surgery and at 3 months postoperatively to evaluate the hearing status. Results: Overall graft uptake rate in Group I was 85%, whereas that in Group II was 95% (P < 0.01). In Group I, graft uptake rate for small perforations was 100%, for medium 85.71%, subtotal 80%, and big central 66.66%. However, Group II graft uptake rates were 100% in all sizes except in medium-sized perforations (83.33%). The air–bone gap gain in Groups I and II was 14.91 (standard deviation [SD] ±9.741) and 14.48 (SD ± 9.366), respectively (P > 0.05). The hearing improvement was statistically insignificant between anterior and posterior perforations. Conclusion: From this study, we observed that size of the perforation is a major factor that influences graft uptake and hearing improvement results in Type I tympanoplasty using reinforced sliced conchal cartilage. Site of perforation failed to be a statistically significant influencing factor in this study.

Keywords: Pure-tone audiometry, reinforced sliced conchal cartilage, temporalis fascia, tympanic membrane perforation, Type I tympanoplasty


How to cite this article:
Singh SP, Nagi RS, Singh J. To study the effect of site and size of tympanic membrane perforation on graft uptake rates and hearing improvement in type I tympanoplasty using sliced conchal cartilage reinforced with temporalis muscle fascia and temporalis muscle fascia alone. Indian J Otol 2019;25:121-6

How to cite this URL:
Singh SP, Nagi RS, Singh J. To study the effect of site and size of tympanic membrane perforation on graft uptake rates and hearing improvement in type I tympanoplasty using sliced conchal cartilage reinforced with temporalis muscle fascia and temporalis muscle fascia alone. Indian J Otol [serial online] 2019 [cited 2019 Nov 12];25:121-6. Available from: http://www.indianjotol.org/text.asp?2019/25/3/121/269557




  Introduction Top


Apart from conduction of sound waves across the middle ear, the tympanic membrane (TM) also serves a protective function to the middle ear cleft and round window niche. Intact TM protects the middle ear cleft from infections and shields the round window from direct sound waves, which is referred to as “round window baffle.”[1] This shield is necessary to create a phase differential so that the sound wave does not impact on the oval and round windows simultaneously. This would dampen the flow of sound energy being transmitted in a unilateral direction from the oval window through the perilymph. It has been found that the effect of the enhanced ratio of the surface area of the TM to that of the oval window increases the sound pressure by about 27 dB, whereas the lever action of ossicles contributes about 3 dB.[2],[3]

A perforation on the TM reduces the surface area of the membrane available for sound pressure transmission and allows sound to pass directly into the middle ear. As a result, the pressure gradient between the “inner” and “outer” surfaces of the membrane virtually becomes insignificant. The effectiveness with which the TM transmits motion to the ossicular chain is thus impaired along with the level of hearing.[4] It has been established that, the larger the perforation of the TM, the greater is the decibel loss in sound perception. A total absence of the TM would lead to a loss in the transformer action of the middle ear.[5] The location of the perforation is believed by some schools of thought to have a significant effect on the magnitude of hearing loss.[6] As posterior-quadrant perforations are believed to be worse than the anterior ones because of the direct exposure of the round window to sound waves, perforations at or near the site of TM attachment to manubrium have more severe effects than those of comparable size at different sites.[6] However, some workers believe that there is no significant effect associated with the location of the perforation.[5],[7] Thus, this is divergent opinion on the study of the correlation between the site and size of central perforation of TM and hearing loss.

A tympanoplasty is fundamentally a tissue transference procedure. Various graft materials have been used to close TM perforations. These graft materials include temporalis fascia, cartilage, perichondrium, periostia, dura mater, vein tissue, fat, and skin.[4],[5] Many previous studies have compared the anatomical and functional outcomes of various graft materials.

In this study, we have compared two graft materials namely temporalis fascia and 0.5-mm thick reinforced conchal cartilage to find anatomical and functional outcomes in Type I tympanoplasty with respect to the size and site of TM perforation in patients with chronic suppurative otitis media (CSOM).

Aims and objectives

To study the effect of the site and size of TM perforation on graft uptake reinforced with temporalis muscle fascia and temporalis muscle fascia alone.


  Materials and Methods Top


In this retrospective study, a total of forty patients presenting with dry central perforation with intact and mobile ossicular chain and conductive type of hearing loss, visiting the ENT outpatient department of Government Medical College, Amritsar, Punjab, India, were included in the study during September 2013–2016. They were randomly divided into two groups of twenty patients each, with Group I patients undergoing Type I tympanoplasty with temporalis muscle fascia and Group II patients with sliced conchal cartilage as graft reinforced with temporalis fascia. A pure-tone audiometry was done 1 week prior to the surgery and at 3 months postoperatively to evaluate the hearing status. Ethical clearance for the study was obtained from the Institutional Ethics Committee, Government Medical College, Amritsar. Patients fulfilling the inclusion criteria were assigned to the study randomly. Consent (informed, written, and well understood) was obtained from each patient. The aims and objectives of the study, the benefits to be obtained, the confidentiality of participants and results, the voluntary nature of participation, and free will to withdraw from the study without penalty were clearly spelt out to the participants.

Inclusion criteria

  1. Dry central perforation for more than a month with remnant of the pars tensa, all around
  2. Intact and mobile ossicular chain
  3. Pure, conductive type of hearing loss.


Exclusion criteria

  1. Ear discharge within the last month prior to surgery
  2. Possibility of cholesteatoma
  3. Presence of granular myringitis
  4. Revision tympanoplasties
  5. Except ear disease, no other disease condition which could affect the result of the study.


Methodology to measure the size of perforation

To measure the size of perforation, we have used a presterilized (cidex) thin transparent sheet, on which a graph paper of 1 mm × 1 mm in size was printed. The measurement of size was done intraoperatively under an operating microscope after performing posterior canal wall meatotomy, before starting the tympanoplasty procedure. The results of this study were compared with those of other studies. The total effective surface area of the TM was taken to be 55 mm2, and the sizes of perforation were categorized as follows:

  1. 1–14 mm2, i.e., 25% of the total effective TM surface area involved by perforation
  2. 15–27 mm2, i.e., 25%–50% of the total effective TM surface area perforated
  3. 28–41 mm2, i.e., 50%–75% of effective TM surface area perforated and
  4. 42–55 mm2, i.e., 75%–100% of effective TM surface area involved by the perforation.


Brief details of surgical procedure to be followed are as follows:

Under standard aseptic conditions, the patients were appropriately draped. The postauricular area and external auditory canal were infiltrated with 1% xylocaine with 1:100,000 adrenaline. In Group I patients, temporalis fascia graft was harvested through the postauricular incision. In patients of Group II, both conchal cartilage graft and temporalis fascia graft were harvested through postauricular incision. The cartilage graft so obtained was thinned with the help of a precise cartilage splitter. Ossicular mobility and continuity were assessed. The handle of malleus was denuded. In patients of Group I, temporalis muscle fascial graft was placed by underlay technique. In Group II patients, the sliced cartilage graft of 0.5-mm thickness was placed by underlay technique in a meticulous manner after filling the middle ear with gel foam. A V-shaped notch was removed from the cartilage to accommodate the malleus handle temporalis fascia will be placed lateral to the sliced conchal cartilage by underlay technique. Antibiotics were continued for 2 weeks and anti-histaminics for 3 weeks. At the end of follow-up period on the 90th postoperative day, the external auditory canal was cleaned, and status of the TM was examined to look for healing/nonhealing of the perforation. Pure-tone audiometry was also performed to evaluate air–bone gap (ABG) closure.


  Results Top


Forty consecutive patients fulfilling the inclusion criteria underwent tympanoplasty between September 2013 and 2016.

Pearson's Chi-square test, paired t-test, unpaired t-test, and correlation study were used to evaluate the results. P < 0.05 was considered statistically significant. In this study, most of the patients belonged to the age group of 15–45 years, with a mean age of 29.30 ± 6.46 years in Group I, whereas a mean age of 27.05 ± 10.44 years in Group II [Table 1].
Table 1: Age-wise distribution of patients

Click here to view


In Group I, the patients were equally divided based on their gender. However, in Group II, 55% were female, whereas 45% were male. The most common symptom was difficulty in hearing (87.5%) of the affected ear; it was mainly of conductive type with 57.5% of patients had mild-degree hearing loss, 30% had moderate-degree hearing loss, and 12.5% had hearing within normal limits. CSOM was the predominant cause of perforation.

In Group I, 35% of the patients had a medium-sized central perforation, 25% of patients had subtotal central and small perforation, whereas only 15% had big central perforation. In Group II, most of the patients (35%) had a small perforation, 30% had medium sized, 20% big central, and 15% subtotal perforation [Graph 1].



Overall graft uptake rate in Group I was 85%, whereas Group II patients had an uptake rate of 95% (P < 0.01). The mean improvement in preoperative pure tone average (PTA), and postoperative PTA values in Group I and II were 14.91 (standard deviation [SD] ±9.741) and 14.48 (SD ± 9.366), respectively (P > 0.05).

In Group I, graft uptake rate for small perforations was 100%; for medium-sized 85.71%; subtotal 80%; and big central 66.66%. However, graft uptake rates in Group II were 100% in all sizes except in medium-sized perforations (83.33%). The average ABG improvement for both Groups I and II was 14.85 dB ± 5.62 SD. The present study showed that there were small differences in the hearing improvements at different frequencies between anterior and posterior perforations (1–5 dB) but were statistically insignificant.


  Discussion Top


Tympanoplasty is a surgical technique for the treatment of patients with chronic otitis media (COM). The goal of tympanoplasty is to eradicate disease and restore the function of the middle ear.[1] The temporal muscle fascia is preferred for being easily accessible, having the possibility of using the same incision, and for bearing low metabolic index. Currently, the perforations that involve up to 40% of the TM and have low-level hearing loss, tragus cartilage has shown great effectiveness.

Many published studies have identified tympanoplasty as a successful procedure for closing TM perforations and improving air conduction hearing. However, the impact of perforation size and site upon tympanoplasty success is not effectively documented. This study was aimed at finding out the effect of site and size of TM perforation on graft uptake rates and hearing improvement in Type I tympanoplasty using sliced conchal cartilage reinforced with temporalis muscle fascia and temporalis muscle fascia alone.

In this study, graft uptake rate in Group I was 85%, whereas Group II patients had an uptake rate of 95%. Loss of graft or partial uptake was present in about 20% of the patients [Graph 2].



In literature, the success rates of tympanoplasty differ widely. Lee et al. in their study “Myringoplasty: Does the size of the perforation matter?” have shown success rate in small perforations to be 74%, but in large perforations, their success rate was only 56%.[8] Avile's Jurado et al. (2009) in their study found success rate for small perforations as 90% and for large perforations as 54.54%.[9] In a study by Vaidya et al., graft was intact in 86 (86%) patients, with a majority of them (91.11%) having small-sized perforation (1–14 mm2) at the end of 3-month follow-up and residual perforation was found in 14 (14%) patients, with a majority (37.5%) of them having subtotal-type (42–55 mm2) perforations.[10]

In a study by Uslu et al., a 78.3% success rate for TM healing was reported. In their study, there were 17 patients whose perforation was >75% of total membrane diameter preoperatively and 15 of them healed with no perforation; 1 of them had a perforation <25% of total membrane diameter and 1 of them had a perforation between 50% and 75% of total membrane diameter. These results show that the cartilage reinforcement technique had a great success rate in subtotal or total perforation. With this technique, cartilage reinforces and supports the temporal fascia graft and prevents the detachment of the fascial graft anteriorly.[11]

In our study results with relation to size of perforation in Group I postoperative graft uptake rate in small perforations was 100%, medium perforations was 85.71%, subtotal was 80%, and big central was 66.66%. However, Group II graft uptake rates were 100% in all sizes except in medium-sized perforation (83.33%). In this study, graft uptake rates according to size were statistically significant (P < 0.001). We observed size of the perforation to be a major factor that influenced the success of Type I tympanoplasty [Table 2].
Table 2: Graft uptake according to the size of tympanic membrane perforation

Click here to view


In our study graft uptake results with relation to site of perforation, we studied that success rate was highest (100%) for posterior, inferior, central perforations, whereas one patients anterior quadrant perforation presented with residual perforation in Group II. In Group I, one anterior quadrant, one subtotal (posterosuperior [PS] + anteroinferior [AI] + posteroinferior [PI]), and one central perforation showed residual perforations; however, success rates for posterior and inferior quadrant were 100%. Graft uptakes among the site in both groups were not statistically significant.

There are several studies examining the effects of the location of the perforation on the surgical outcome. In the study by Vaidya et al., maximum graft intactness was observed in single-quadrant perforations at an average of 93.22% and maximum residual perforations at an average of 33.33%, where all the four quadrants were involved.[10] Jurovitzki et al. stated that an anterior perforation was less favorable than perforations seen in other locations.[12] Frade González et al. observed better success for posterior perforations and weaker success for subtotal perforations.[13] Albera et al. showed that risk of tympanic residual perforation is more common in posterior perforations,[14] whereas Onal et al. reported that the success rate of the anterior, posterior, and central perforations showed no difference.[15] In our study, TM closure rate and hearing improvement were not associated with the location of perforation, similar to other studies.[16],[17]

Hearing improvement after surgery in relation to the size of perforation

We studied that perforation-induced hearing losses were generally greatest at the lowest frequencies and decreased as frequency increased. The size of the perforation was also an important determinant of hearing loss. Larger perforations resulted in greater hearing loss, an effect that was present at all audiometric frequencies.

In our study, maximum number of ears, i.e., 7 in Group I and 6 in Group II had size of TM perforation between 15 and 27 mm (25%–50%) of effective surface area with an average hearing improvement of 13.34 dB in Group I and 14.60 dB in Group II, whereas larger perforations involving 42–55 mm (75%–100%) of effective TM surface area suffered from an average hearing improvement of 12 dB in Group I and 14.25 dB in Group II [Table 3].
Table 3: Hearing improvement according to the size of tympanic membrane involvement, i.e., area occupied by perforation (n=40)

Click here to view


It was observed that maximum number of ears had the three quadrants involved by the perforation, i.e., 5 (25%) in Group I and 3 (15%) in Group II and on correlating the hearing improvement according to the site of TM perforation, maximum average hearing improvement 18 dB in Group I and 19 dB in Group II was observed in the perforations involving the three quadrants [Table 2]. In perforations occupying <25% of TM surface area, the difference in mean average hearing improvement was 11 dB in Group I and 9.18 dB in Group II, which was statistically insignificant (P > 0.05). Vaidya et al. observed an average hearing improvement of 14.03 dB in small-sized perforations, 16.08 dB hearing improvement in medium-sized perforations, 15 dB in large-sized perforations, and 16.25 dB hearing improvement in subtotal perforations.[10] Deosthale et al. reported that average hearing improvement was more in subtotal perforations (19.25 dB) as compared to small-sized perforations (6.03 dB).[18]

Khan et al.'s study concluded that reinforcement of temporalis fascia with sliced tragal cartilage is a reliable technique for tympanoplasty, especially in large perforations without affecting audiometric results.[19] Zhang et al. demonstrated that, after myringoplasty for small perforation of the TM (<50%), ABG is minimum (average 5.5 dB) and most ABG (average 10.5 dB) was after the closure of large perforations (>50%).[20]

We studied that, in concern of the audiological parameters, the difference between preoperative and postoperative hearing levels was statistically significant (P < 0.001). Thus, there was no statistically significant improvement in mean PTA (dB) gain in Group I as compared to Group II.

Hearing improvement after surgery in relation to the site of perforation

The posterior perforations result in larger hearing losses than anterior perforations preoperatively. The explanation for this view has been that perforations over the round window result in a sound pressure acting at the round window that diminishes the cochlear response by a “phase cancellation effect.”

In the present study, in Group I, single-quadrant (Anteroinferior) perforations and (Posteroinferior) had equal average hearing improvement of 11 dB postoperatively, whereas Group II had a difference of nearly 3 dB [Table 4].
Table 4: Hearing improvement according to the site of tympanic membrane perforation

Click here to view


In the present study, in Group I, two-quadrant perforation (AS + AI) showed 18.16 dB, PS + PI showed 13.99 dB, and AI + PI showed 11.79 dB. Group II had 13.33 dB hearing improvement in AS + AI, 15.33 dB in PS + PI, and 12.58 dB in AI + PI quadrants.

In three-quadrant perforation, PS + PI + AI had hearing improvement of 18 dB in Group I and 19 dB in Group II, which was almost the same in both groups of our study.

Perforations of all the four quadrants in this study had shown a difference of 2 dB in both groups. The present study showed that there were small variations in hearing improvement (1–5 dB) according to the different quadrants of TM perforation in both groups, but statistically insignificant differences in the mean PTA gain between anterior and posterior perforations.

In the study by Deosthale et al., average hearing improvement was more in PI quadrant perforation than AS and AI quadrant perforations. Average hearing improvement was greater in perforations involving all the four quadrants (AS + AI + PS + PI).[18] These results are consistent with Vaidya et al.'s[10] study, in which average hearing improvement in PI quadrant perforation was of 17.04 dB. In AS quadrant perforation, hearing improvement was of 12.94 and in all four quadrant perforations, hearing improvement was of 16 dB.[11] Mehta et al.[21] and Oluwole and Mills[22] did not observe significant difference in average hearing loss in anterior versus posterior quadrant perforations.

The statistical analysis of the locations of tympanic perforation in patients with pure conductive hearing loss showed no correlation with the magnitude of hearing losses recorded. This suggests that the position of the tympanic perforations does not affect the resultant magnitude of conductive hearing loss.[23],[24] This is in consonance with the reports of Voss et al. and other workers whose results showed no effect of position of the TM perforation on hearing loss.[25],[26],[27]


  Conclusion Top


Success of Type I tympanoplasty depends on the preoperative perforation size as a major factor. In this study, graft uptake rates according to the size were statistically significant (P = 0.001), especially in large perforations and without affecting audiometric results of reinforced sliced conchal cartilage and temporalis fascia alone. The site of perforation on the TM has no effect on the magnitude of hearing improvement as well as in graft uptake results.


  Summary Top


Reconstruction of different TM perforations mostly large or subtotal perforation is always a challenge to the otologist. Although temporalis fascia and reinforced sliced conchal cartilage can both effectively be used for the above purpose, sliced cartilage graft is thought to be the superior autograft compared with temporalis fascia for bigger size perforations along with better graft uptake. Although cartilage grafting is somewhat difficult and time-consuming, it can be considered as the first-line treatment in COM with large/subtotal perforations, with satisfactory outcomes.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Ogisi FO, Adobamen P. Type 1 tympanoplasty in benin: A 10- year review. Niger Postgrad Med J 2004;11:84-7.  Back to cited text no. 1
    
2.
Voss SE, Rosowski JJ, Merchant SN, Peake WT. Non-ossicular signal transmission in human middle ears: Experimental assessment of the “acoustic route” with perforated tympanic membranes. J Acoust Soc Am 2007;122:2135-53.  Back to cited text no. 2
    
3.
Shamb Baugh GE. From Surgery of the Ear. Philadelphia: W.B. Saunders; 1959. p. 336-7.  Back to cited text no. 3
    
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Krunger T. Tympanic-membrane perforation in cats with experimentally induced tympanic-membrane perforation. J Acoust Soc Am 1978;63:436-41.  Back to cited text no. 4
    
5.
American Academy of Otolaryngology-Head and Neck: Perforated Ear Drum; 2005. Available from: http://www.entnet.org/HealthInformation/perforatedEardrum.cfm. [Last accessed on 2007 May 07].  Back to cited text no. 5
    
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Ahmad SW, Ramani GV. Hearing loss in tympanic membrane perforations. J Laryngol Otol 1979;93:1091-8.  Back to cited text no. 6
    
7.
Roland NJ, McRae RD, McCombe AW. From chronic suppurative otitis media. In: Key Topics in Otolaryngology and Head and Neck Surgery. 2nd ed. Wales: BIOS Scientific Publishers; 2001. p. 38-41.  Back to cited text no. 7
    
8.
Lee P, Kelly G, Mills RP. Myringoplasty: Does the size of the perforation matter? Clin Otolaryngol Allied Sci 2002;27:331-4.  Back to cited text no. 8
    
9.
Avile's Jurado FJ, Meran Gil JL, Tobed Secall M, Domexnech Vadillo E, Masgoret Palau E, Martıxnez Novoa MD, et al. Myringoplasty: Auditory follow up and study of prognostic factors. Acta Otorrinolaringol Esp 2009;60:169-75.  Back to cited text no. 9
    
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Vaidya S, Sharma JK, Singh G. Study of outcome of tympanoplasties in relation to size and site of tympanic membrane perforation. Indian J Otolaryngol Head Neck Surg 2014;66:341-6.  Back to cited text no. 10
    
11.
Uslu C, Tek A, Tatlipinar A, Kiliçarslan Y, Durmuş R, Ayöǧredik E, et al. Cartilage reinforcement tympanoplasty: Otological and audiological results. Acta Otolaryngol 2010;130:375-83.  Back to cited text no. 11
    
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Jurovitzki I, Sadé J. Myringoplasty: Long-term followup. Am J Otol 1988;9:52-5.  Back to cited text no. 12
    
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Frade González C, Castro Vilas C, Cabanas Rodríguez E, Elhendi W, Vaamonde Lago P, Labella Caballero T, et al. Prognostic factors influencing anatomic and functional outcome in myringoplasty. Acta Otorrinolaringol Esp 2002;53:729-35.  Back to cited text no. 13
    
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Albera R, Ferrero V, Lacilla M, Canale A. Tympanic reperforation in myringoplasty: Evaluation of prognostic factors. Ann Otol Rhinol Laryngol 2006;115:875-9.  Back to cited text no. 14
    
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Onal K, Uguz MZ, Kazikdas KC, Gursoy ST, Gokce H. A multivariate analysis of otological, surgical and patient-related factors in determining success in myringoplasty. Clin Otolaryngol 2005;30:115-20.  Back to cited text no. 15
    
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Lima JC, Marone SA, Martucci O, Gonçalez F, Silva Neto JJ, Ramos AC, et al. Evaluation of the organic and functional results of tympanoplasties through a retro-auricular approach at a medical residency unit. Braz J Otorhinolaryngol 2011;77:229-36.  Back to cited text no. 16
    
17.
Karela M, Berry S, Watkins A, Phillipps JJ. Myringoplasty: Surgical outcomes and hearing improvement: Is it worth performing to improve hearing? Eur Arch Otorhinolaryngol 2008;265:1039-42.  Back to cited text no. 17
    
18.
Deosthale NV, Kumar P, Khadakkar SP, Harkare VV, Dhoke PR, Dhote KS, et al. Outcome of type I tympanoplasty in tubotympanic chronic suppurative otitis media in relation to site and size of tympanic membrane perforation. J Evol Med Dent Sci 2015;4:15834-8.  Back to cited text no. 18
    
19.
Khan MM, Parab SR. Reinforcement of sliced tragal cartilage perichondrium composite graft with temporalis fascia in type I tympanoplasty: Our Techniques and results. J Rhinolaryngo Otol 2013;1:57-62.  Back to cited text no. 19
    
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Zhang ZG, Huang QH, Zheng YQ, Sun W, Chen YB, Si Y. Three autologous substitutes for myringoplasty: A comparative study. Otol Neurotol 2011;32:1234-8.  Back to cited text no. 20
    
21.
Mehta RP, Rosowski JJ, Voss SE, O'Neil E, Merchant SN. Determinants of hearing loss in perforations of the tympanic membrane. Otol Neurotol 2006;27:136-43.  Back to cited text no. 21
    
22.
Oluwole M, Mills RP. Tympanic membrane perforations in children. Int J Paediatr Otorhinolaryngol 1996;36:117-23.  Back to cited text no. 22
    
23.
Voss SE, Rosowski JJ, Merchant SN, Thornton AR, Shera CA, Peake WT, et al. Middle ear pathology can affect the ear-canal sound pressure generated by audiologic earphones. Ear Hear 2000;21:265-74.  Back to cited text no. 23
    
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25.
Hsu CY, Chen YS, Hwang JH, Liu TC. A computer program to calculate the size of tympanic membrane perforations. Clin Otolaryngol Allied Sci 2004;29:340-2.  Back to cited text no. 25
    
26.
Voss SE, Rosowski JJ, Merchant SN, Peake WT. Acoustic responses of the human middle ear. Hear Res 2000;150:43-69.  Back to cited text no. 26
    
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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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